How does Java solve retain cycles in garbage collection?

Question

I know that a retain cycle (at least in Objective-C and Swift) is when two objects claim ownership of one another (they have references to each other). And in Objective-C we can

Answer 1

In basic terms, Garbage Collection works by walking the object graphs from a number of predefined roots. Anything not accessible from those roots is garbage, therefore one object referencing another is irrelevant unless either can be accessed from one or more roots.

It's all explained in more detail in How Garbage Collection Really Works.